In process measurements and automation technology, for measuring physical parameters, such as e.g. the mass flow, respectively the mass flow rate, the volume flow, respectively the volume flow rate, as well as the density and/or the viscosity, of media flowing in pipelines, often such measuring systems are used—most often measuring systems formed as in-line measuring devices in compact construction—, which by means of a measuring transducer of vibration-type flowed-through by the medium and a measuring and driver circuit connected therewith, bring about reaction forces in the medium, such as e.g. Coriolis forces corresponding to the mass flow, inertial forces corresponding to the density of the medium and/or frictional forces corresponding to the viscosity of the medium, etc., and, derived from these forces, produce a measurement signal representing the respective mass flow, viscosity and/or density of the medium. Such measuring transducers, respectively measuring systems formed therewith, especially embodied in the form of Coriolis mass flow meters or Coriolis mass flow/densimeters, are described at length and in detail e.g. in CN-A 10 18 58 765, EP-A 1 001 254, EP-A 816 807, EP-A 553 939, US-A 2002/0157479, US-A 2006/0150750, US-A 2006/0162468, US-A 2007/0151368, US-A 2008/0047361, US-A 2010/0242623, US-A 2011/0016991, US-A 2011/0146416, US-A 2011/0154914, US-A 2011/0265580, US-2011/0113896, US-A 2012/0048034, US-A 2012/0073384, US-A 2012/0079891, US-A 2012/0090407, US-A 2012/0109543, US-A 2012/0167697, U.S. Pat. No. 4,777,833, U.S. Pat. No. 4,793,191, U.S. Pat. No. 4,801,897, U.S. Pat. No. 4,823,614, U.S. Pat. No. 4,879,911, U.S. Pat. No. 5,009,109, U.S. Pat. No. 5,024,104, U.S. Pat. No. 5,050,439, U.S. Pat. No. 5,370,002, U.S. Pat. No. 5,796,011, U.S. Pat. No. 5,804,741, U.S. Pat. No. 6,311,136, U.S. Pat. No. 6,308,580, U.S. Pat. No. 6,311,136, U.S. Pat. No. 6,415,668, U.S. Pat. No. 6,711,958, U.S. Pat. No. 6,920,798, U.S. Pat. No. 7,134,347, U.S. Pat. No. 7,392,709, U.S. Pat. No. 7,992,452, WO-A 00/57141, WO-A 01/067052, WO-A 03/027616, WO-A 2008/039203, WO-A 2011/008307, WO-A 2011/008308, WO-A 2011/019344, WO-A 2011/068500, WO-A 2012/028425, WO-A 90/15309, WO-A 90/15310, WO-A 94/21999, WO-A 96/05484, WO-A 97/33150, WO-A 98/038479 and also the not pre-published German patent application 102011089808.5.
Each measuring transducer includes a housing, of which an inlet-side first housing end is formed at least partially by means of a first flow divider having at least two, in each case, mutually spaced, circularly cylindrical or conical, flow openings and an outlet-side second housing end formed at least partially by means of a second flow divider having at least two, in each case, mutually spaced, flow openings. In the case of some of the measuring transducers shown in U.S. Pat. No. 5,796,011, U.S. Pat. No. 7,350,421, US-A 2007/0151368, US-A 2011/0146416, US-A 2011/0146416 and e.g. US-A 2011/0265580, the housing comprises a rather thick walled, circularly cylindrical, tube segment, which forms at least a middle segment of the housing.
For guiding the medium, which flows at least at times and which is, in given cases, also multiphase, the measuring transducers comprise, furthermore, in each case, two—in the case, for instance, of US-A 2011/0146416, US-A 2011/0146416, respectively US-A 2011/0265580 four—measuring tubes, which are connected for flow through in parallel and composed of metal, especially steel or titanium, which are placed within the housing and held oscillatably therein by means of the aforementioned flow dividers. The measuring tubes thus form a vibration element and are, at times, also referred to as the inner part. A first of the equally-constructed and mutually parallel measuring tubes communicates with an inlet-side first measuring tube end with a first flow opening of the inlet-side first flow divider and with an outlet-side second measuring tube end with a first flow opening of the outlet-side second flow divider and a second of the measuring tubes communicates with an inlet-side first measuring tube end with a second flow opening of the first flow divider and with an outlet-side second measuring tube end with a second flow opening of the second flow divider. In the case of US-A 2011/0146416, US-A 2011/0146416, respectively US-A 2011/0265580, moreover, a third of the measuring tubes communicates with an inlet-side first measuring tube end with a third flow opening of the first flow divider and with an outlet-side second measuring tube end with a third flow opening of the second flow divider and a fourth of the measuring tubes communicates with an inlet-side first measuring tube end with a fourth flow opening of the first flow divider and with an outlet-side second measuring tube end with a fourth flow opening of the second flow divider. Each of the flow dividers includes, furthermore, in each case, a connecting flange with a sealing surface for the fluid tight connecting of the measuring transducer to line segments of the pipeline serving for supplying medium, respectively removing medium, from the measuring transducer.
The measuring tubes, consequently the vibration element formed therewith, are, for producing the above-mentioned reaction forces, caused to vibrate during operation, driven by at least one oscillation exciter serving for producing, respectively maintaining, mechanical oscillations, especially bending oscillations, of the measuring tubes in the so-called driven, or wanted, mode. The oscillations in the wanted mode (wanted mode oscillations) are most often, especially in the case of application of the measuring transducer as a Coriolis mass flow- and/or densimeter, embodied at least partially as lateral bending oscillations of each of the measuring tubes, in each case, about an imaginary oscillation axis, and, in the case of medium flowing through the measuring tubes, as a result of Coriolis forces induced therein, as additional, superimposed oscillations of equal frequency in the so-called Coriolis mode (Coriolis mode oscillations). Accordingly, the exciter mechanism, most often an electrodynamic exciter mechanism, in the case straight measuring tubes, is embodied in such a manner that therewith the at least two measuring tubes are excitable in the wanted mode at least partially, especially also predominantly, to opposite equal, consequently opposite equal bending oscillations, in a shared plane of oscillation differentially—thus by action of exciter forces acting simultaneously along a shared line of action, however, in opposed directions.
For registering vibrations of the vibration element, especially bending oscillations of the measuring tubes excited by means of the exciter mechanism, and for producing oscillation measurement signals representing vibrations of the vibration element, measuring transducers of the aforementioned type have, furthermore, in each case, a sensor arrangement, most often likewise an electrodynamic vibration sensor arrangement, reacting to relative movements of one or more of the measuring tubes. Typically, the vibration sensor arrangement is formed by means of an oscillation sensor registering inlet-side oscillations of the measuring tubes differentially—thus only relative movements of the measuring tubes—as well as an oscillation sensor registering outlet-side oscillations of the measuring tubes differentially, wherein each generates, dependent on vibrations of the vibration element, an oscillatory signal, which has a signal frequency corresponding to the instantaneous oscillation frequency of the vibration element, in such a manner that between the oscillatory signal of the inlet-side oscillation sensor and the oscillatory signal of the outlet-side oscillation sensor a relative phase difference exists dependent on the instantaneous mass flow rate. Each of the oscillation sensors, which are usually constructed equally to one another, is formed by means of a permanent magnet held on the first measuring tube and a cylindrical coil held on the second measuring tube and permeated by the magnetic field of the permanent magnet.
In operation, the above-described vibration element of the measuring transducer formed by means of the at least two measuring tubes is excited by means of the electro-mechanical exciter mechanism at least at times in the wanted mode to execute mechanical oscillations at at least one dominating, wanted, oscillation frequency. Selected as oscillation frequency for the oscillations in the wanted mode, in such case, is usually a natural instantaneous resonant frequency of the vibration element, which, in turn, essentially depends both on an eigenfrequency of the vibration element determined by, among other things, size, shape and material of the vibration element, as well as also on an instantaneous density of the medium contacting the vibration element. In given cases, this wanted oscillation frequency can be influenced significantly by an instantaneous viscosity of the medium. As a result of fluctuating density of the medium to be measured and/or as a result of media changes performed during operation, the wanted oscillation frequency during operation of the measuring transducer is naturally variable at least within a calibrated and, insofar, predetermined wanted frequency band, which has corresponding, predetermined, lower and upper limit frequencies. Based on the currently excited wanted oscillation frequency, namely an instantaneous resonant frequency of the vibration element, accordingly also the density of the medium can be ascertained with such measuring systems, respectively based on a combination of the wanted oscillation frequency and the mentioned phase difference between the oscillation signals of the oscillation sensors, also a volume flow rate, respectively a volume flow, can be ascertained with such measuring systems. For defining a free oscillatory length of the measuring tubes and, associated therewith, for adjusting the wanted frequency band, measuring transducers of the above-described type most often further comprise, for forming inlet-side oscillation nodes for opposite-equal vibrations, especially bending oscillations, of the two measuring tubes, at least one inlet-side coupling element, which is affixed to both measuring tubes spaced from the two flow dividers, as well as, for forming outlet-side oscillation nodes for opposite-equal vibrations, especially bending oscillations, of the measuring tubes, at least one outlet-side coupling element, which is affixed to both measuring tubes spaced both from the two flow dividers as well as also from the inlet-side coupling element. The coupling elements can additionally also influence an oscillation quality factor of the inner part, as well as also the sensitivity of the measuring transducer as a whole.
The respective measuring transducer is, furthermore, connected with a measuring and operating electronics of the measuring system serving for evaluation of the at least one oscillation measurement signal and for generating corresponding measured values representing, for example, the mass flow rate, the volume flow rate or the density. In the case of modern measuring systems of the type being discussed, such measuring and operating electronics, such as, for example, described in the above mentioned U.S. Pat. No. 6,311,136, are most often implemented by means of one or more microprocessors formed, in given cases, also as digital signal processors (DSP). Besides evaluating the oscillation measurement signal, the measuring and operating electronics serves also for generating at least one, for example, harmonic and/or clocked, driver signal for the at least one oscillation exciter acting on the vibration element, wherein the driver signal can be embodied as a broadband signal having a signal component with a signal frequency matching the resonant frequency of the vibrating element or, for example, also as a rather narrow band or harmonic signal with a single dominating signal component of matching signal frequency. Said signal component, respectively the driver signal as a whole, can be controlled, for example, as regards electrical current and/or voltage level. In the case of measuring systems of the type being discussed, the measuring and operating electronics is most often accommodated within at least one comparatively robust, especially impact-, pressure-, and/or weather resistant, electronics housing. The electronics housing can be arranged, for example, remotely from the measuring transducer and be connected with such only via a flexible line; it can, however, also, such as shown e.g. also in the above mentioned U.S. Pat. No. 5,796,011, be arranged directly on the measuring transducer or on a measuring transducer housing separately housing the measuring transducer, consequently its vibrating element. Moreover, it is, however, such as, among other things, shown in WO-A 01/29519, also quite usual, in given cases, to use modularly formed electronics accommodated in two or more separate housing modules for forming measuring systems of the type being discussed. Usually, the respective measuring and operating electronics is, furthermore, electrically connected via corresponding electrical lines to a superordinated electronic data processing system arranged most often spatially removed from the respective measuring system and most often also spatially distributed. The measured values produced by the respective measuring system are forwarded to the electronic data processing system near in time by means of a measured value signal correspondingly carrying the measured values. Measuring systems of the type being discussed are additionally usually connected by means of a data transmission network provided within the superordinated data processing system with one another and/or with corresponding electronic process controllers, for example, on-site programmable logic controllers or process control computers installed in a remote control room, where the measured values produced by means of the respective measuring system and digitized and correspondingly coded in suitable manner are forwarded. By means of such process control computers, the transmitted measured values can be further processed and visualized as corresponding measurement results e.g. on monitors and/or converted into control signals for other field devices, such as e.g. magnetically operated valves, electric motors, etc., embodied as actuating devices. Since modern measuring systems can most often be so directly monitored and, in given cases, controlled and/or configured from such control computers, operating data intended for the measuring system are equally sent in corresponding manner via the aforementioned data transmission networks, which are most often hybrid as regards the transmission physics and/or the transmission logic. Accordingly, the data processing system serves usually also to process the measured value signal delivered by the measuring system corresponding to the requirements of downstream data transmission networks, for example, suitably to digitize the signal and, in given cases, to convert it into a corresponding telegram, and/or on-site to evaluate it. For such purpose, there are provided in such data processing systems, electrically coupled with the respective connecting lines, evaluating circuits, which pre- and/or further-process, as well as, in case required, suitably convert, the measured values received from the respective measuring system. Serving for data transmission in such industrial data processing systems, at least sectionally, are fieldbusses, especially serial fieldbusses, such as e.g. FOUNDATION FIELDBUS, RACKBUS-RS 485, PROFIBUS, etc. fieldbusses, or, for example, also networks based on the ETHERNET standard, as well as the corresponding, most often comprehensively standardized, transmission protocols. Alternatively or supplementally, in the case of modern measuring systems of the type being discussed, measured values can be transmitted wirelessly per radio to the particular data processing system. Besides the evaluating circuits required for processing and converting the measured values delivered from the respectively connected measuring systems, such superordinated data processing systems have most often for supplying the connected measuring systems with electrical energy also electrical supply circuits, which provide, in given cases, directly fed from the connected fieldbus, a corresponding supply voltage for the respective measuring and operating electronics and drive the electrical currents flowing through the thereto connected electrical lines as well as the respective measuring and operating electronics. A supply circuit can, in such case, for example, be associated with exactly one measuring system, respectively a corresponding measuring and operating electronics, in each case, and together with the evaluating circuit associated with the respective measuring system, for example, united to form a corresponding fieldbus adapter, and be accommodated in a shared electronics housing, e.g. an electronics housing in the form of a top hat rail module. It is, however, also quite usual to accommodate supply circuits and evaluating circuits, in each case, in separate electronics housings, in given cases, electronics housings spatially remote from one another, and to connect them with one another correspondingly via external lines.
Development in the field of measuring systems with measuring transducers of vibration-type has reached a state, in which modern measuring systems of the described type can for a very broad application spectrum of flow measurement technology satisfy highest requirements as regards precision and reproducibility of measurement results. Thus, such measuring transducers, respectively the measuring systems formed therewith, are in practice applied for mass flow rates from only a few g/h (gram per hour) up to several t/min (tons per minute), in the case of pressures up to 10 MPa (megapascal) for liquids or even over 30 MPa for gases. The accuracy of measurement achieved, in such case, lies usually at, for instance, 99.9% of the actual value or more, respectively a measuring error of, for instance, 0.1%, wherein a lower limit of the guaranteed measurement range can lie at, for instance, 1% of the measurement range end value. Due to the high bandwidth of their opportunities for use, industrial grade measuring systems with measuring transducers of vibration-type are available with nominal diameters (corresponding to the caliber of the pipeline to be connected to the measuring transducer, respectively the caliber of the measuring transducer measured at the connecting flange), which lie in a nominal diameter range between 0.5 mm and 400 mm (millimeter) and at maximum nominal mass flow rate, for example, also of greater than 3000 t/h, in each case, with pressure losses of less than 0.1 MPa. A caliber of each measuring tube can in the case of large nominal diameters easily be greater than 80 mm.
In spite of the fact that, in the meantime, measuring transducers for use in pipelines with very high mass flow rates and, associated therewith, very large calibers of far above 100 mm are becoming available, there is still a significant interest in obtaining measuring transducers of high precision and low pressure loss also for yet larger pipeline calibers, for instance, 450 mm or more, respectively mass flow rates of 3000 t/h or more. Particularly the measuring transducers shown in the above mentioned US-A 2011/0265580 with a vibration element having four bent measuring tubes are without doubt suitable to be able to fulfill the requirements of, consequently to be able to be designed for, large nominal diameters from over 450 mm. This not least of all also in applications, in which also the volume flow rate, respectively the volume flow, are of special interest, such as, for instance, for applications in the petrochemicals industry or in the field of transport and handling of petroleum, natural gas, fuels, etc.
However, in industrial plants having pipelines with, at times, relatively tightly dimensioned lateral spacings between pipelines guiding the medium and thereto neighboring plant components, such conditions can significantly make difficult, respectively, at times, completely exclude use of measuring transducers, respectively measuring systems, having, depending on the manner of construction, comparatively large lateral dimensions. In contrast, such measuring transducers with four straight measuring tubes, such as are described, for example, in the above mentioned WO-A 2012/028425, US-A 2011/0146416, US-A 2012/0073384, US-A 2012/0079891, US-A 2012/0227512, can, in comparison to those with bent measuring tubes, in the case of equal nominal diameter clearly be dimensioned more compactly, whereby their use for applications with limited available space are, initially, definitely indicated. Measuring transducers of vibration-type, in the case of which the vibration element has straight measuring tubes, show, such as, among other things, also mentioned in US-A 2012/0073384, respectively U.S. Pat. No. 4,823,614, however, in comparison to such, in the case of which the vibration element is formed by means of two or more bent measuring tubes, an increased cross-sensitivity to mechanical loadings, be it from clamping forces introduced via the pipeline—mainly axial clamping forces, namely forces acting in the direction of the imaginary oscillation axis, respectively a measuring tube longitudinal axis parallel thereto—, respectively therefrom resulting mechanical stresses in the vibration element or through mechanical stresses in the vibration element as a result of thermally related, elastic deformation of the measuring tubes. This, such as already discussed in the mentioned US-A 2012/0073384, is quite true also for the case, in which the vibration element is formed by means of four straight measuring tubes, of which each has a caliber of greater than 60 mm.
Although the clamping forces have for the accuracy of measurement, with which mass flow, respectively the mass flow rate, is ascertained, only a small, respectively with little effort, for instance, by application of temperature- and/or strain sensors, compensable influence, the influence of clamping forces, respectively the therefrom resulting mechanical stresses in the vibration element, on the accuracy of measurement in the case of the density measurement is quite significant. Associated therewith, accordingly also the volume flow rate, respectively the volume flow derived therefrom, can have a correspondingly fluctuating accuracy of measurement. Making this more difficult is the fact that in measuring systems of the type being discussed the clamping forces are potentially larger, the higher is the mass flow rate nominally to be measured therewith, respectively the greater are the nominal diameters. Thus, applications, in which there is more an interest in precise measuring of high volume flow, respectively high volume flow rates, then in the precise ascertaining of mass flows, respectively mass flow rates, can lead, at times, to no longer tolerable measuring inaccuracies in the case of measuring systems of the type being discussed.